This invention concerns a dose setting device for self-use medical injectors of the kind having a knob at the rear end which is rotated, before use, by an amount that determines the dose that is to be dispensed. Generally, such a knob is knurled or ribbed for a good grip and when rotated it clicks round over a ratchet mechanism. A sequence of numbers around its periphery indexes past a datum mark on the barrel of the injector, the user ceasing to rotate the knob when the number representing the required dose registers with that mark. The mark is often a raised stud, of arrowhead form for example. When the injector is fired, the knob is released and is returned to its initial position with zero opposite the mark. Such an injector is sold under the Registered Trade Mark AUTOPEN.
While it is commercially sensible to have an injector capable of being set to dispense a wide range of doses, each individual user is likely to be prescribed a set dose, and therefore the knob of his injector is always rotated the same amount before each injection. It is the aim of this invention to make the pre-setting operation easy and almost automatic every time.
According to one aspect of the present invention there is provided a dose setting device for medical injectors of the kind having a rotary dose setting knob at the rear end of a barrel that can be indexed around from a zeroed position to bring an indicator opposite a mark on a scale, the device comprising an annular member adapted to fit retentively over the dose setting knob in any of a plurality of relative rotational positions each corresponding to a selected dose, and having an abutment which can co-operate with a raised stud on the barrel, rotation of the knob for dose setting being arrested by the abutment meeting the stud with the indicator opposite the selected dose mark.
In the preferred form the annular member is the mouth portion of a cup that press fits over and covers the knob.
Conveniently the scale is on the knob and the annular member is adapted to leave at least part of the scale visible.
However, it is possible for the annular member to be adapted for the scale being on the barrel, the stud being at the zero point thereof, and the indicator being on the knob.
According to another aspect of the present invention there is provided a dose setting device for medical injectors of the kind having a rotary dose setting knob at the rear end of a barrel that can be indexed around from a zeroed position to bring an indicator opposite a mark on a scale, the device comprising an annular member adapted to fit retentively over the rear end of the barrel in any of a plurality of relative rotational positions each corresponding to a selected dose, and having an abutment which can co-operate with a raised stud on the knob, rotation of the knob for dose setting being arrested by the stud meeting the abutment with the indicator opposite the selected dose mark.
The annular member is adapted for the scale being on the knob, the stud being at the zero point thereof, and the indicator being on the barrel.
Alternatively, the scale may be on the barrel, in which case the annular member will preferably be adapted to leave at least part of the scale visible.
When the annular member is so adapted, whether it is on the knob or the barrel, it may be opaque, except for a window through which the selected dose mark may be seen.
Alternatively, the annular member could be a unitary moulding of transparent plastics material, with a short section thickened into a magnifying lens for placement over the selected dose number.
In either case the indicator is conveniently provided is by the stud and the abutment projects from the annular member immediately adjacent the window or lens.